For photoelectric conversion devices, such as photovoltaic cells and semiconductor lasers, use of quantum dots has been proposed recently to enhance the photoelectric conversion efficiency. Representative examples of quantum dots that are utilized for photoelectric conversion devices, such as photovoltaic cells, include semiconductor nanoparticles having a size of approximately 10 nm. When semiconductor nanoparticles are to be used as quantum dots for photovoltaic cells, the semiconductor nanoparticles need to have a passivation film (e.g., aluminum oxide) on a surface thereof.
Examples of methods for forming such an inorganic passivation film include atomic layer deposition (hereinafter referred to as ALD).
ALD is performed as follows. Semiconductor nanoparticles are deposited on a substrate to form an integrated film, and a vaporized organometallic compound, together with a gas such as oxygen, is spayed on top of the integrated film. Thus, an inorganic material is formed between the semiconductor nanoparticles (see, for example, Non-Patent Literature 1).
In such a case, a surface treatment for enhancing dispersibility is performed on the semiconductor nanoparticles for forming a photoelectric conversion film, to enable the semiconductor nanoparticles to be arranged at high density when being deposited on the substrate. For example, low molecular weight organic molecules, referred to as ligands, may be applied to surfaces of the semiconductor nanoparticles. A composite material may be thus formed and used. Further, an inorganic material is formed to fill a region around each of such semiconductor nanoparticles and organic molecules.